1. Technical Field of the Invention
The present invention relates in general to the wireless communication systems field, and in particular, to a method and system for improving channel quality in wireless communication systems.
2. Description of Related Art
Benefits of mobile wireless communications are safety, convenience, and efficiency. To maximize the enjoyment of these benefits, the quality of transmitted voice signals should be optimized. Voice quality in today's digital communication systems depends primarily on the coding process employed to digitize speech. One parameter affecting voice quality is the number of bits per second transmitted by a given speech coding technique (e.g., using vocoders, waveform coders, hybrid coders, etc.). Generally, the higher the bit rate, the better the voice quality.
Unfortunately, as the bit rate is increased, the transmission bandwidth demanded by the speech coding technique is also increased. In a cellular wireless communications system, the transmission bandwidth between the mobile terminals and a base station is finite. This finite transmission bandwidth is best utilized in existing cellular systems by assigning channels that can accommodate the speech coding technique with the lowest-possible bit rate.
A conventional traffic channel assignment method is for a base station to receive a request from a mobile terminal for a traffic channel. The associated cellular system then determines the lowest-possible traffic bit rate. The mobile terminal's call is then assigned to a channel that uses the lowest-possible traffic bit rate.
The problem with the existing cellular systems is that the lowest-possible traffic rate channel often corresponds to the use of a sub-optimum speech coding technique. In other words, the associated cellular system requires the use of a speech coding technique with fewer bits per second, in order to minimize the amount of the total available bandwidth occupied by a single call from a mobile terminal. Unfortunately, reduced speech quality accompanies the use of a lower-rate speech coding technique. Furthermore, existing cellular systems typically select a lower-rate speech coding technique for a call even when significant bandwidth capacity in a given cell is available. For example, a half-rate traffic channel is used to gain capacity in the network, and today a half-rate channel is always assigned when the mobile terminal is capable of half-rate, the call is between the mobile terminal and the Public Switched Telephone Network (PSTN), and the call is a speech call.
In summary, conventional traffic channel assignment methods assign the lowest-possible traffic rate channel to a mobile terminal at the expense of transmitted voice quality.